ATrain1

I am trying to figure out what the easiest differential swap would be in my 1979 Cutlass. I want to go to either a 8.2 or an 8.5 from a 7.5 gm rear end do to strength issues. I will be running about 500 HP and 500 ft pounds of torque. Thanks for your help.

gearheads78

Order a 9" or a Stange S60 and be done with it. By the time you spend the money on a 8.5 you still need to weld the housing, install good axles and c clip eliminators. You said you are going to run a trans brake. Do it once and do it right.

olds 307 and 403

9" is definitely the way to go. I blew up my 7.5" with maybe 300 hp and 375 ft/lbs.

Funkwagon455

True.......

Rickman48

9" is overkill and a little heavy, IMO.
12-bolt, set up correctly, will handle it!

gearheads78

He has a g-body. 8.5 is just as stong as a 12 bolt but then see my first post. Factory 12bolts do not bolt in without custom control arms and will still need all the upgrades a 8.5 does. 9" is not over kill for a motor that already makes 500 HP. If he is anything like most racers its never enough. Wait until he puts two kits on it. Small plate to get going and a nice fogger to keep things moving

Rickman48

And a 9" Furd bolts right in?
Needs nothing?

I agree - stronger, and if he had a bigger car, fine, but with a G-body, at about 3800 max, a 12-bolt will probably save some money that could be used elsewhere!
Guess I can't 'read between the lines' about a trans brake or nitrous, either!

gearheads78

back when I had my G-body it was cheaper to by a bolt in 9" housing than to build a 12 bolt. In fact the first version of it cost me about $500.00 I bought a complete rear out of a truck and a bolt in 9" housing. Had the axles cut down and drilled for GM pattern and swapped it all over. Back when it was a mild 400 hp street car and worked fine. When I sold it it was close a 900 hp car and still had the same bolt in housing but of course by then it was all trick internals... MW aluminum center, 35 spine axles, Wilwood brakes ect. Another really cool thing about the 9" is how easy it is to swap gears. When I went in Power Tour in it all I had to do is swap in a different carrier with highway friendly 3.50 gears and next weekend back to the 4.30's

random examples
http://www.quickperformance.com/Products/housings.htm

http://www.moserengineering.com/comp...figurator.html

ATrain1

I am trying to get it down to 3300 as well. I had no idea a Ford 9 inch would bolt right in.

What kind of car would be the best to pull it out of? I like the idea of running a 9 inch and being able to change gears like that. The last time I messed with a rear end was in my brothers 1965 Buick special. I believe the rear end was out of a 69-72 Cutlass wagon and it would not fit without a lot of work. I understand I am going to have a lot of work into this car anyway, any place I can get a break and still do it right would be great. Thanks for your replies.

ATrain1

Hey guys is there anything I can do to make my 7.5 rear differential strong enough so I can run this year? I have a lot of people coming out to watch me race from the Springs and all over, so I would really like to run. I am willing to take advice and not run this rear end if it is going to possibly hurt me or my car, I just do not have the time to change my rear end and have a drive shaft made. I was thinking to start with a C-clip eliminator kit with a set of 28 spline axles with my locker. Also I could skip the burn out box and not run it as hard as I usually would, and use regular tires instead of slicks.

2blu442

Read through this thread and check out the video. I'd say you should do the rear end before racing!

https://classicoldsmobile.com/forums...ded-video.html

ATrain1

My friend has a 12 bolt rear differential out of a 1969 or 1970 Cutlass. My question is what would it take to bolt it into my G-body? Is it worth it? Or would it cost more than it is worth? Thanks

gearheads78

Not worth it. Not a bolt in deal and still would need work.

Nasty455

I had the same problem with the Le Mans I bought.
Previous owner tried to graft in a 73-77 version.
They are totally different.
The drive line did not line up,as the rear pinion was canted upwards and the spring perches were wrong.

monzaz

8.8 Ford G-body rear Moser Billet end uses ford Large axle bearing and race axles. Same width as stock g-body 78-88

upper control arms are slightly different than g-body but i make uppers that are double adjustable and spherical ends for bind free articulation.

Jim
JD

gearheads78

there you go Atrain....even comes from a member of the board

Rickman48

And cost vs Strange bolt-in 12-bolt Chevy?
Is it stronger? [8.8 vs 8.875]

ATrain1

Hey Jim could you Pm me the more info on that please? I am very interested in that and would like to know that cost shipped to me. Thanks